This invention relates to an oxygen sensor used in detecting the oxygen concentration in a gas such as the exhaust gas from an internal combustion engine of automotive vehicles. More particularly, it relates to a solid electrolyte consisting essentially of completely stabilized, sintered zirconia, which has a good thermal shock resistance.
Among the solid electrolytes of this sort for use in an oxygen sensor, there has been known a sintered body of stabilized zirconia which is prepared by mixing zirconia with a stabilizer such as yttria, calcia, or ytterbia followed by sintering at high temperatures, as disclosed in U.S. Pat. No. 4,219,359 (Miwa et al.).
A solid electrolyte made of the completely stabilized, sintered zirconia has such a defect that it exhibits a poor thermal shock resistance to a rapid change in temperature.
The inventors have discovered that this defect is predominently caused by the structural coarseness of the completely stabilized, sintered zirconia crystals.